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I

868

Appendix IL

which is the small increase of tension for arc 0n.    Hence we may
write

dt = pie*       and  = p 0n

Summating each side of the equation separately, over the whole
angle,

Bat if

og,,

.}    _.   Tn=

and Log io

P. 555. Friction.  Experiments on  solid  friction may be
classified under six heads : 

4.  Journal friction.

5.  Collar friction.

6.  Pivot friction.

1.  Static friction.

2.  Friction at low speeds.

3.  Friction at high speeds.

And in every case the surfaces may be wholly or partially
lubricated, may be dry, or may be coated with a resistant. The
first three are usually taken with flat surfaces, and the results
known as (flat friction/ unit pressure being constant over the
surface. In the remaining cases the surface pressure may be
very unequal.

The friction at starting, called friction of repose or static
friction, has been but little examined, but some good results
were obtained in 1895 by Mr. Broomall, of America, being the
averages of twenty or thirty trials with each load.

VALUES OF     FOR STATIC FRICTION.

Material.
	Dry.
	Wet.

Cast iron on cast iron    ...
	'3"4
	3401

Steel on steel      .........
	4408
	

Steel on cast iron
	2303
	

Cast iron on tin ...
	'454 T
	

Steel on tin
	3648
	

Cast iron on pine           ...     ....
	4702
	

Pine on pine
	4738
	"6350